In semiconductor producing processes, in order to form a wiring pattern on a semiconductor wafer as a substrate (which will be hereinafter referred to as a “wafer”) or in order to fill in a hole between wiring portions, a metal or metal compound, such as W, WSi (tungsten silicide), Ti (titanium), TiN (titanium nitride) or TiSi (titanium silicide), is deposited to form a thin film.
When a W thin film is deposited, SiH4 (silane) gas is fed to carry out a pretreating called initiation prior to the deposition. It is an object of the initiation to absorb SiHx (e.g. x=1 to 3) on a wafer prior to the formation of the W film so as to form a uniform W film without abnormal grain growth thereon.
However, there are conventional problems in that, when such an initiation process is carried out, abnormal grain growth is caused during the deposition of the W film, or the surface condition of the W film is deteriorated, due to the influence of the type of the under layer or the surface condition or due to the influence of conditions in the processing vessel. Such problems are remarkable particularly when a low temperature process on a wiring pattern, such as a bit line, is carried out or when a thin film having a thickness of about 100 nm is formed.
In order to eliminate such abnormal grain growth and/or deterioration of the surface condition, a nucleation process is carried out at the beginning of the deposition of the W film. However, in this case, the margin of process conditions is very small, so that it is difficult to stably produce a film having a good surface condition.